1. Technical Field
The present disclosure relates to a display device, and in particular to a display device having an organic light-emitting diode.
2. Description of the Related Art
Recently, with the development and wide application of electronic products, such as mobile phones, and notebook computers, there has been increasing demand for flat display elements which consume less power and occupy less space. Organic light-emitting diodes (OLEDs) are popular for use in flat-panel displays as they are self-emitting and highly luminous, provide wide viewing angles, have a fast response speed, and enjoy a simple fabrication process.
An organic light-emitting diode is an LED that uses an organic layer as the active layer. In recent years, organic light-emitting diodes have been gradually employed in flat-panel displays. One trend in organic light-emitting diode technology is for achieving higher luminescent efficiency and a longer life span.
Generally, an organic light-emitting diode is composed of a light-emitting layer sandwiched between a pair of electrodes. When an electric field is applied to the electrodes, the cathode injects electrons into the light-emitting layer and the anode injects holes into the light-emitting layer. When the electrons recombine with the holes in the light-emitting layer, excitons are formed. Recombination of the electron and hole results in light emission.
In accordance with driving methods, an organic light-emitting diode device is a passive matrix type or an active matrix type. The active matrix organic light-emitting diode (AM-OLED) device is driven by electric currents, in which each of the matrix-array pixel areas has at least one thin film transistor (TFT), to control the brightness and gray level of the pixel areas. The thin film transistors can be a p-type transistor or an n-type transistor. The active matrix organic light-emitting diode device has a panel luminescence with thin and lightweight characteristics, and a spontaneous luminescence with high luminance efficiency and low driving voltage.
When a standard organic light-emitting diode (the term “standard organic light-emitting diode” means that an organic light-emitting diode includes an anode, a hole injection layer, hole transport layer, light-emitting layer, electron transport layer, electron injection layer, and a cathode sequentially formed on a substrate) is coupled to an n-type transistor to form an organic light-emitting diode device, the standard organic light-emitting diode has to electrically connect to a source electrode of the n-type transistor. Hence, an image sticking phenomenon is apt to be observed occur during operation of the aforementioned organic light-emitting diode device.
To solve above-mentioned problems, an organic light-emitting diode device including an inverted organic light-emitting diode (the term “inverted organic light-emitting diode” means that an organic light-emitting diode includes a cathode, an electron injection layer, an electron transport layer, a light-emitting layer, a hole transport layer, a hole injection layer, and an anode sequentially formed on a substrate) coupled to a drain electrode of an n-type transistor. The inverted organic light-emitting diode, however, exhibits lower luminous efficiency and higher driving voltage in comparison with standard organic light-emitting diodes with the same layers due to the inferior electron injection characteristic.
Therefore, an organic light-emitting diode device capable of increasing luminous efficiency and reducing driving voltage is desirable.